1. Field of the Invention
The invention relates to the steam reforming of fluid hydrocarbons. More particularly, it relates to an improved process and apparatus for reducing the fuel consumption and waste heat requirements of steam reforming operations.
2. Description of the Prior Art
In conventional steam reforming of fluid hydrocarbons, the feed material is conveniently passed through catalyst-containing vertically hanging reformer tubes maintained at an elevated temperature by radiant heat transfer and/or by contact with combustion gases in the furnace of the tubular reactor. The hot reformer tube effluent may be passed to a waste heat recovery zone for the generation of steam that can be used in the steam reforming operations.
Such conventional operations are commonly carried out at temperatures of from about 800.degree. C. to about 900.degree. C. with a mole ratio of steam to hydrocarbon feed of from about 2/1 to about 4/1. While such operations have been effectively carried out in practical commercial operations, there is a genuine need in the art for improved processes and apparatus to reduce the fuel consumption and waste heat requirements of steam reforming operations and to reduce the capital investment costs of such operations. This need is particularly acute in light of the rapidly increasing cost of fuel employed in such operations.
Various processing techniques and apparatus have, of course, been disclosed in the art with respect to hydrocarbon reforming and cracking operations. For example, the Bongiorno patent, U.S. Pat. No. Re. 24,311, discloses conventional steam reforming with the use of the exhaust gas from the gas turbine used to compress the product synthesis gas as a combustion-supporting gas to heat the primary reformer furnace that produces the synthesis gas. Orr, U.S. Pat. No. 2,519,696, discloses a horizontally oriented tube cracking furnace in which gases to be cracked pass through and are preheated in horizontal tubes and exit therefrom into direct contact with hot combustion gases. The resulting gas stream passes through cracking tubes countercurrently to the feed gases. The invention is said to provide a maximum thermal heat exchange relationship in which the gases to be cracked are preheated before being subject to reaction heat conditions, with the incoming feed likewise cooling the reaction mixture so as to prevent undesirable side reactions. With respect to high pressure cracking operations, Woebcke et al, U.S. Pat. No. 3,910,768, teaches the desirability of permitting the process fluid and the combustion gas to operate at essentially the same pressure, thereby relieving the pressure differential on the reactor tubes. Hanging reactor tubes are provided in the convection section with processing fluids passing downward therein countercurrent to the upward flow of flue gas.
A heat exchanger-tubular steam reformer is disclosed by Kydd, U.S. Pat. No. 3,607,125, in which process gas passes downwardly through an annular, catalyst-filled space between a metal liner and a centrally located product tube and thereafter rises upward in said tube. The reactor tube is hung vertically with the thermal stress thereon being minimized since the lower end by the tube is not connected to any supporting structure. Kydd discloses that the direction of process flow through the apparatus can be reversed, with the process gas entering the centrally located hanging tube and exiting, after passage downward through the catalyst, in an upward direction along the annular space between the tube and the wall of the apparatus.
Such prior art developments illustrate the desire to effectively utilize the available waste heat from reforming and cracking operations and to reduce the fuel requirements of such operations. There remains a need for further developments of this type, however, particularly to reduce the need for waste heat recovery, as by steam generation, in applications in which there is little need for export steam.
It is an object of the present invention, therefore, to provide an improved process and apparatus for the steam reforming of fluid hydrocarbons.
It is another object of the invention to provide a steam reforming process and apparatus capable of permitting desirable reductions in the fuel consumption and waste heat requirements of such reforming operations.
It is a further object of the invention to provide for the effective utilization of the heat generated in the steam reforming of fluid hydrocarbons.
With these and other objects in mind, the invention is hereinafter described with reference to particular embodiments thereof, the novel features of which are particularly pointed out in the appended claims.